It's an interesting question, because "theft" seems to mean that someone has some ownership rights, while "public domain" seems to mean that the rights are owned by "the public."
If the file isn't public domain, then the copyright owner needs to file a claim to remove the file. If the file is public domain, then there was no theft. If the file isn't public domain, but the copyright owner doesn't file a claim to remove the file, then the file is an "orphaned" work, which has been discussed elsewhere in archive.org
But to say that someone stole a public domain file from someone is oxymoronic.